Structure and catalytic function of sphingosine kinases: analysis by site-directed mutagenesis and enzyme kinetics.

Sphingosine kinases 1 and 2 (SK1 and SK2) generate the bioactive lipid mediator sphingosine 1-phosphate and as such play a significant role in cell fate and in human health and disease. Despite significant interest in and examination of the role played by SK enzymes in disease, comparatively little is currently known about the three-dimensional structure and catalytic mechanisms of these enzymes. To date, limited numbers of studies have used site directed mutagenesis and activity determinations to examine the roles of individual SK residues in substrate, calmodulin, and membrane binding, as well as activation via phosphorylation. Assays are currently available that allow for both single and bisubstrate kinetic analysis of mutant proteins that show normal, lowered and enhanced activity as compared to wild type controls. Additional studies will be required to build on this foundation to completely understand SK mediated substrate binding and phosphoryl group transfer. A deeper understanding of the SK catalytic mechanism, as well as SK interactions with potential small molecule inhibitors will be invaluable to the future design and identification of SK activity modulators as research tools and potential therapeutics. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.